Process for producing olefins

ABSTRACT

The present invention provides a process for producing olefins from a feed comprising at least methane, ethane and carbon dioxide. The feed is separated into at least a methane-comprising feed, an ethane-comprising feed and a carbon dioxide-comprising feed. At least part of the methane-comprising feed is converted to a synthesis gas. The ethane-comprising feed is cracked to obtain at least olefins and hydrogen. At least part of the carbon dioxide-comprising feed and at least part of the synthesis gas are used to synthesis oxygenates. At least part of the oxygenates are converted in an oxygenate-to-olefin (OTO) zone to obtain at least olefins and hydrogen. At least part of the cracking effluent and at least part of the OTO zone effluent are combined to obtain a combined effluent from which hydrogen is separated. At least part of the hydrogen is supplied to the oxygenate synthesis zone.

This application claims the benefit of European Application No.09175607.2 filed Nov. 10, 2009 which is incorporated herein byreference.

FIELD OF THE INVENTION

The invention relates to a process for producing olefins and anintegrated system for producing olefins.

BACKGROUND OF THE INVENTION

In recent years increasing attention is given to the exploration andutilisation of natural gas resources around the globe. A disadvantage ofnatural gas with respect to oil is the difficulty to transport largevolumes of natural gas from the source to the market. One way ofefficiently transporting natural gas is by liquefying the natural gasand to transport the liquefied natural gas (LNG). Another way is toconvert the methane in the natural gas to liquid hydrocarbons using aGas-to-Liquid process (GtL). The GtL products are typically liquid andcan be transported in a similar way as traditional oil and oil products.

Besides methane, the natural gas typically comprises other hydrocarbonssuch as ethane, propane, and butanes. Such a natural gas is referred toas wet gas. The latter two can be added to the LPG pool, however, ethanecannot. Moreover, for various reasons the ethane content in the naturalgas supplied to an LNG or GtL process is restricted and therefore asignificant part of the ethane must be removed from the natural gasprior to providing the natural gas to either a LNG or GtL process.

Although, the application of ethane is limited, typically ethane iscombusted in a furnace to provide heat; its corresponding olefinethylene is a base chemical with a wide application and is of greatcommercial interest. Ethane can be converted into ethylene, e.g. using athermal cracking process. Subsequently, the ethylene can be used toproduce e.g. polyethylene, styrene or mono-ethylene-glycol. Theconversion of ethane to ethylene is highly endothermic and requiressignificant energy input. In addition, the capex for the ethane toethylene process, in particular the back-end work-up section, and thesubsequent ethylene conversion processes is high and a minimum ethyleneproduction capacity is required to make it economically benign.

When, the ethane content in the natural gas is too low, and consequentlyinsufficient ethane is available, the ethane/ethylene route becomesunattractive.

This problem becomes even more pronounced, in the case where the naturalgas is withdrawn from relatively small reservoirs, especially thoselocated in remote isolate locations, also revered to as stranded naturalgas. Of course, this stranded natural gas may be converted to LNG or GtLproducts. However, this requires the stranded gas reservoir to sustain aminimum production level per day in order to make the investmentsworthwhile. Typically, such stranded natural gas reservoirs cannotachieve sufficient production levels to sustain a GtL or LNG plant. Inaddition, insufficient ethane is co-produced to sustain an ethane toethylene process and subsequent ethylene conversion processes.

It has been suggested to combine an ethane steam cracker withOxygenate-to-Olefin (OTO) processes, which can produce additionalethylene. For instance, C. Eng et al. (C. Eng, E. Arnold, E Vora, T.Fuglerud, S. Kvisle, H. Nilsen, Integration of the UOP/HYDRO MTO Processinto Ethylene plants, 10^(th) Ethylene Producers' Conference, NewOrleans, USA, 1998) have suggested to combine UOP's Methanol-to-Olefins(MTO) process with a naphtha or ethane fed steam cracker. It ismentioned that by combining both processes sufficient ethylene can beproduced, while coproducing valuable propylene. A disadvantage mentionedby C. Eng et al. is the fluctuating price of methanol, which is theprimary feed to the MTO reaction.

In WO 2009/039948 A2, a combined stream cracking and OTO process issuggested for preparing ethylene and propylene. According to WO2009/039948 A2, in this process, a particular advantage is obtained bycombing the back-end of both processes. The methanol feedstock isproduced from methane, requiring a sufficient supply of methane.

In US2005/0038304, an integrated system for producing ethylene andpropylene from an OTO system and a steam cracking system is disclosed.According to US2005/0038304, in this process, a particular advantage isobtained by combining the back-end of both processes. The methanolfeedstock to the OTO process is produced from synthesis gas. However,according to US2005/0038304 the production of methanol from synthesisgas has high energy requirements due to the endothermic nature of thesynthesis gas production process, such an endothermic synthesis gasproduction process is normally steam methane reforming.

In US2002/0143220A1, a process is described for producing olefins. Ahydrocarbon feedstock is oxidatively dehydrogenated to produced olefinsand synthesis gas. The synthesis gas may be converted to methanol. Themethanol may be converted to ethylene.

A problem with using natural gas to produce ethylene is that togetherwith the hydrocarbons in the natural gas a substantial amount of carbondioxide may be co-produced from the subsurface natural gas or oilreservoir. Such carbon dioxide is also referred to as field carbondioxide. Some subsurface natural gas or oil reservoirs comprisesubstantial concentrations of carbon dioxide, up to 70 mol % based onthe total content of the gas extracted from the reservoir. This carbondioxide must be sequestrated or otherwise captured and stored.

An additional problem is that, especially when the carbon dioxidecontent is high, not enough ethane is produced from the subsurfacereservoir to sustain a ethane cracker with full work-up section.

In US2007/049647A1 it is described that carbon dioxide co-produced withnatural gas may be mixed with synthesis gas to produce a methanol feedfor a methanol-to-olefins process.

In WO2007/142739A2, a process is described for producing methanol fromsynthesis gas. The methanol may be used for producing olefins. In theprocess described in WO2007/142739A2, a hydrogen stream comprisinggreater than 5 mol % methane is combined with the synthesis gas. Thehydrogen stream may for instance be obtained from a steam crackingprocess. According to WO2007/142739A2 it is desirable that the amount ofCO2 in the synthesis gas feedstock is minimized to reduce the need forlater separation of water from the crude methanol.

There is a need in the art for a process for producing ethylene from afeed comprising, besides hydrocarbons, carbon dioxide, wherein theamount of carbon dioxide that needs to be sequestrated or otherwisecaptured and stored is further reduced.

SUMMARY OF THE INVENTION

It has now been found that it is possible to further reduce the amountof carbon dioxide that needs to be sequestrated or otherwise capturedand stored, when producing ethylene from a feed comprising, besideshydrocarbons, carbon dioxide by using an integrated process, wherein atleast part of the field carbon dioxide together with hydrogen producedinternally by the process is used to synthesis oxygenates that can beused as feedstock to an OTO process.

Accordingly, the present invention provides a process for producingolefins, comprising:

a. providing a feed comprising at least methane, ethane and carbondioxide;

b. separating the feed into at least a methane-comprising feed, anethane-comprising feed and a carbon dioxide-comprising feed;

c. providing at least part of the methane-comprising feed to a processfor preparing synthesis gas to obtain a synthesis gas;

d. cracking the ethane-comprising feed in a cracking zone under crackingconditions to obtain a cracking zone effluent comprising at leastolefins and hydrogen;

e. providing at least part of the carbon dioxide-comprising feed and atleast part the synthesis gas obtained in step c) to an oxygenatesynthesis zone and synthesising oxygenates;

f. converting at least part of the oxygenates obtained in step (e) in anoxygenate-to-olefin zone to obtain an oxygenate-to-olefin effluentcomprising at least olefins and hydrogen;

g. combining at least part of the cracking zone effluent and at leastpart of the OTO zone effluent to obtain a combined effluent;

h. separating hydrogen from the combined effluent and providing at leastpart of the hydrogen to the oxygenate synthesis zone in step (e).

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic representation of an integrated system forproducing olefins according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The process according to the present invention is directed at producingolefins, in particular lower olefins (C2-C4), more in particularethylene and propylene. Several processes, such as ethane cracking orOxygenate-to-Olefin (OTO) processes can produce olefins. The ethanecracking and the OTO processes typically produce ethylene from differentstarting materials. In the case of the ethane cracking step, the feed ispreferably an ethane-comprising feed. The OTO step on the other handuses an oxygenate-comprising feed. Preferred oxygenates includealkylalcohols and alkylethers, more preferably methanol, ethanol,propanol and/or dimethylether (DME), even more preferably methanoland/or dimethylether (DME).

By using an integrated process comprising both an ethane crackingprocess and an OTO process it is possible to produce lower olefins froma mixed feed comprising both methane and ethane. Such a feedstock isfirst separated into a methane-comprising feed and an ethane-comprisingfeed. The ethane-comprising feed is used as feed to the ethane crackingprocess. The methane-comprising feed is converted to synthesis gas,which is used to synthesize the oxygenate-comprising feed required forthe OTO process.

The most common feedstock comprising both methane and ethane is naturalgas. Besides methane and ethane, the natural gas may contain significantamounts of carbon dioxide. This carbon dioxide is contained in thesubsurface reservoir from which the natural gas is produced. As thenatural gas is withdrawn from the reservoir the carbon dioxide isco-produced as part of the natural gas.

There is a desire not to emit this coproduced carbon dioxide to theatmosphere, therefore it must be sequestrated or otherwise captured andstored.

It has now been found that by producing olefins by an integrated processcomprising an ethane cracking step and an Oxygenate-to-Olefin (OTO)step, a synergetic use of the feedstock comprising at least methane,ethane and carbon dioxide is achieved by using at least part of thecarbon dioxide that is in the feedstock, further also referred to asfield carbon dioxide for synthesising oxygenates, preferably byconverting hydrogen with carbon monoxide and/or carbon dioxide intomethanol and/or dimethylether. Wherein at least part of the hydrogen isco-produced in the ethane cracking step and OTO step.

These oxygenates are subsequently fed to the OTO reaction to formfurther olefins.

By using field carbon dioxide the need to sequestrate or otherwisecapture and store the field carbon dioxide is reduced if not omitted. Atleast part of the field carbon dioxide is used to produce at least partof the oxygenate feed to the OTO zone. As a result, the field carbondioxide is no longer dissipated into the atmosphere or otherwisecaptured and stored, but rather used to produce valuable oxygenates.Thereby, the carbon dioxide penalty for producing the olefins isreduced.

In addition, the field carbon dioxide preferably does not comprisesignificant amounts of inerts such as N₂ or Ar. These inerts maytypically be present in the natural gas or purified oxygen provided toproduce synthesis gas for methanol production. By providing field carbondioxide as part of the feed to the oxygenate synthesis zone the inertcontent in this feed may be reduced.

By providing at least part of the field carbon dioxide to the oxygenatesynthesis zone the amount of synthesis gas needed to synthesise theoxygenates may be reduced. The synthesis gas is typically produced bypartial oxidation of hydrocarbons using essentially pure oxygen or atleast oxygen enriched air. The production of pure oxygen is highlyenergy consuming, therefore a reduction in the synthesis gas demand alsoreduces the oxygen demand, which in return results in decreased energyconsumption and carbon dioxide production. Moreover, the capitalinvestment can be reduced as a smaller oxygen production unit isrequired.

In the process according to the invention a feedstock comprising atleast methane, ethane and carbon dioxide is provided. In step (b) of theprocess, the feedstock is separated into at least a methane-comprisingfeed, an ethane-comprising feed and a carbon dioxide-comprising feed.Hereinbelow the carbon dioxide-comprising feed will also be referred toas carbon dioxide ex. field.

In step (c) of the process, at least part of the methane-comprising feedis provided to a process for preparing synthesis gas. Such processes forpreparing synthesis gas preferably include non-catalytic partialoxidation processes, catalytic partial oxidation processes, steammethane reforming processes, auto-thermal reforming processes, andwater-gas-shift processes, wherein hydrocarbons, in particular methaneare converted with oxygen and optionally steam to at least hydrogen andpreferably carbon monoxide. Although, a water-gas-shift process is inprinciple not a process for preparing a synthesis gas, the effluent of awater-gas-shift process typically comprises carbon monoxide, carbondioxide and hydrogen. The methane-comprising feed may be provided toseveral processes for preparing synthesis gas.

The methane-comprising feed may be converted into a synthesis gas havinga hydrogen and carbon monoxide and/or carbon dioxide molar ratio, asdefined hereinbelow:molar ratio=(#mol H₂−#mol CO₂)/(#mol CO+#mol CO₂),

Preferably, the methane-comprising feed is converted in to a synthesisgas having a hydrogen and carbon monoxide and/or carbon dioxide molarratio, which is above the ratio preferred for synthesising methanol,i.e. sources that are carbon deficient.

As can be seen in the definition of the molar ratio hereinabove, awater-gas-shift does not influence the molar ratio obtained.

Preferably, a synthesis gas is used comprising little or no carbondioxide. When using a synthesis gas with little or no carbon dioxide,more carbon dioxide ex. field can be added. Low carbon dioxidecomprising synthesis gases are therefore preferred, more preferred aresynthesis gases comprising carbon dioxide in the range of from 0 to 8mol % even more preferably of from 0.1 to 3 mol %, still even morepreferably 0.2 to 2.5 mol %, based on the total number of moles in thesynthesis gas.

Such low carbon dioxide synthesis gases are preferably produced by noncatalytic partial oxidation processes for preparing synthesis gas. Apartial oxidation catalyst typically induces some water-gas-shift in thepresence of water. As a result carbon monoxide is shifted to carbondioxide. An additional advantage is that non-catalytic partial oxidationprocesses do not require the addition of substantial amounts of water tothe process. Such as non-catalytic partial oxidation processes.Processes producing substantial amounts of carbon dioxide include forinstance Steam Methane Reforming. Therefore, the use of a synthesis gasfrom a Steam Methane Reforming process is less preferred.

In step (d) of the process according to the invention theethane-comprising feed is provided to a cracking zone and cracked undercracking conditions. The obtained cracking product comprises olefins andhydrogen, in particular at least ethylene and hydrogen.

In step (e) of the process according to the invention at least part ofthe carbon dioxide ex. field and at least part the synthesis gasobtained in step c) are provided to an oxygenate synthesis zone. Next tocarbon dioxide ex. field and synthesis gas obtained in step c) othersuitable sources of hydrogen, carbon monoxide and or/carbon dioxide maybe provided to the oxygenate synthesis zone of step (e).

In the oxygenate synthesis zone, oxygenates are preferably synthesisedby reacting hydrogen with carbon dioxide and optionally carbon monoxide.Preferably, hydrogen is reacted with carbon dioxide and optionallycarbon monoxide to form an oxygenate suitable to serve as a feed to anOTO process, in particular alkylalcohols and alkylethers, preferablymethanol and/or di-methyl-ether (DME).

Methanol may be produced directly from hydrogen and carbon dioxide inthe oxygenate synthesis zone. Hydrogen can react with carbon dioxide toproduce methanol following:CO₂+3H₂→CH₃OH+H₂O.

Preferably, the synthesis gas provided to the oxygenate synthesis zonealso comprises carbon monoxide. The hydrogen may than also react withcarbon monoxide to also form methanol following:CO+2H₂→CH₃OH.

Preferably, the carbon dioxide, hydrogen and preferably carbon monoxideare provided to the oxygenate synthesis zone in a molar ratio in therange of from 2.0 to 3.0, preferably 2.0 to 2.2. The molar ratio hereinis defined as:molar ratio=(#mol H₂−#mol CO₂)/(#mol CO+#mol CO₂).

In case a carbon monoxide is present to convert the hydrogen tomethanol, it is preferred that the carbon dioxide concentration in thehydrogen, carbon monoxide and carbon dioxide mixture is in the range offrom 0.1 to 25 mol %, preferably 3 to 15 mol %, more preferably of from4 to 10 mol %, based on the total number of moles hydrogen, carbonmonoxide and carbon dioxide in the mixture. The carbon dioxide content,relative to that of CO, in the syngas should be high enough so as tomaintain an appropriately high reaction temperature and to minimize theamount of undesirable by-products such as paraffins. At the same time,the relative carbon dioxide to carbon monoxide content should not be toohigh so that the reaction of carbon dioxide with hydrogen yields lessmethanol based on the hydrogen provided to the oxygenate synthesis zone.In addition, the reaction of carbon dioxide with hydrogen yields water.If present in too high a concentration, water may deactivate theoxygenate synthesis catalyst.

In the oxygenate synthesis zone the hydrogen, carbon dioxide andpreferably carbon monoxide are converted to methanol in the presence ofa suitable catalyst. Such catalysts are known in the art and are forinstance described in WO 2006/020083, which is incorporated herein byreference. Suitable catalysts for the synthesis of methanol fromhydrogen, carbon dioxide and preferably carbon monoxide include:

-   -   An oxide of at least one element selected from the group        consisting of copper, silver, zinc, boron, magnesium, aluminium,        vanadium, chromium, manganese, gallium, palladium, osmium and        zirconium.    -   Preferably, the catalyst is a copper and zinc based catalyst,        more preferably in the form of copper, copper oxide, and zinc        oxide.    -   A copper based catalyst, which includes an oxide of at least one        element selected from the group consisting of silver, zinc,        boron, magnesium, aluminium, vanadium, chromium, manganese,        gallium, palladium, osmium and zirconium.    -   Preferably, the catalyst contains copper oxide and an oxide of        at least one element selected from the group consisting of zinc,        magnesium, aluminium, chromium, and zirconium.    -   A catalyst selected from the group consisting of: copper oxides,        zinc oxides and aluminium oxides. More preferably, the catalyst        contains oxides of copper and zinc.    -   A catalyst comprising copper oxide, zinc oxide, and at least one        other oxide.

Preferably, the at least one other oxide is selected from the groupconsisting of zirconium oxide, chromium oxide, vanadium oxide, magnesiumoxide, aluminum oxide, titanium oxide, hafnium oxide, molybdenum oxide,tungsten oxide, and manganese oxide.

Particular suitable catalysts include catalysts comprising in the rangeof from 10 to 70 wt % copper oxide, based on total weight of thecatalyst. Preferably, comprising in the range of from 15 to 68 wt %copper oxide, and more preferably of from 20 to 65 wt % copper oxide,based on total weight of the catalyst.

Such catalyst may preferably also contain in the range of from 3 to 30wt % zinc oxide, based on total weight of the catalyst. Preferably, itcontains in the range of from 4 to 27 wt % zinc oxide, more preferablyfrom 5 to 24 wt % zinc oxide, based on total weight of the catalyst.

Catalyst comprising both copper oxide and zinc oxide, preferablycomprise copper oxide and zinc oxide in a ratio of copper oxide to zincoxide which may vary over a wide range. Preferably, such catalystcomprises copper oxide to zinc oxide in a Cu:Zn atomic ratio in therange of from 0.5:1 to 20:1, preferably from 0.7:1 to 15:1, morepreferably from 0.8:1 to 5:1.

The catalyst can be prepared according to conventional processes.Examples of such processes can be found in U.S. Pat. Nos. 6,114,279;6,054,497; 5,767,039; 5,045,520; 5,254,520; 5,610,202; 4,666,945;4,455,394; 4,565,803; 5,385,949, with the descriptions of each beingfully incorporated herein by reference.

Methanol may be synthesised in the oxygenate synthesis zone by anyconventional methanol synthesis process. Examples of such processesinclude batch processes and continuous processes. Continuous processesare preferred.

Tubular bed processes and fluidized bed processes are particularlypreferred types of continuous processes.

The methanol synthesis process is effective over a wide range oftemperatures. Preferably, methanol is synthesised in the oxygenatesynthesis zone by contacting the hydrogen, carbon dioxide and preferablycarbon monoxide with the catalyst at a temperature in the range of from150 to 450° C., more preferably from 175 to 350° C., even morepreferably from 200 to 300° C.

The methanol synthesis process is effective over a wide range ofpressures. Preferably, the methanol is synthesised by contacting thehydrogen, carbon dioxide and preferably carbon monoxide with thecatalyst in the oxygenate synthesis zone at a pressure in the range offrom 15 to 125 atmospheres, more preferably from 20 to 100 atmospheres,more preferably from 25 to 75 atmospheres.

For methanol synthesis, gas hourly space velocities in the oxygenatesynthesis zone vary depending upon the type of continuous process thatis used. Preferably, gas hourly space velocity of flow of gas throughthe catalyst bed is in the range of from 50 hr⁻¹ to 50,000 hr⁻¹.Preferably, gas hourly space velocity of flow of gas through thecatalyst bed is in the range of from about 250 hr⁻¹ to 25,000 hr⁻¹, morepreferably from about 500 hr⁻¹ to 10,000 hr⁻¹.

A methanol synthesis process as described hereinabove may produceseveral oxygenates as by-products, including aldehydes and otheralcohols. Such by-products are also suitable reactants in the OTOreaction. Other less desirable by-products may be removed from theeffluent of the oxygenate synthesis zone effluent if required prior toproviding the oxygenate synthesis zone effluent to the OTO zone as toform at least part of the oxygenate feed.

Another suitable and preferred oxygenate, which may be synthesised inthe oxygenate synthesis zone is dimethylether (DME). DME can be directlysynthesized from synthesis gas, but is preferably synthesized frommethanol. Optionally, DME is obtained from methanol and hydrogen, carbondioxide and preferably carbon monoxide. The conversion of methanol toDME is known in the art. This conversion is an equilibrium reaction. Inthe conversion the alcohol is contacted at elevated temperature with acatalyst. In EP-A 340 576 a list of potential catalysts are described.These catalysts include the chlorides of iron, copper, tin, manganeseand aluminium, and the sulphates of copper, chromium and aluminium. Alsooxides of titanium, aluminium or barium can be used. Preferred catalystsinclude aluminium oxides and aluminium silicates. Alumina isparticularly preferred as catalyst, especially gamma-alumina. Althoughthe methanol may be in the liquid phase the process is preferablycarried out such that the methanol is in the vapour phase. In thiscontext the reaction is suitably carried out at a temperature of 140 to500° C., preferably 200 to 400° C., and a pressure of 1 to 50 bar,preferably from 8-12 bar, the exact choice depends on the acidity of thecatalyst. In view of the exothermic nature of the conversion of methanolto DME the conversion is suitably carried out whilst the reactionmixture comprising the first catalyst is being cooled to maximize DMEyield. Suitably, the methanol to DME reaction takes place in a separatesection of the oxygenate synthesis zone.

In the case where part of the methanol synthesized is converted intoDME, the effluent of the oxygenate zone may comprise methanol and DME inany ratio. Preferably, the ratio of DME to methanol weight ratio is inthe range of from 0.5:1 to 100:1, more preferably from 2:1 to 20:1.Suitably the methanol to DME conversion reaction is led to equilibrium.This includes that the DME to methanol weight ratio may vary from 2:1 to6:1. Evidently, the skilled person may decide to influence theequilibrium by applying different reaction conditions and/or by addingor withdrawing any of the reactants.

In the process according to the invention at least part of the oxygenatefeed is methanol and/or DME produced by reacting field carbon dioxidewith at least a synthesis gas.

In step (f) of the process according to the invention at least part ofthe oxygenates obtained in step (e) are provided to anoxygenate-to-olefin zone and converted to obtain at least olefins. Nextto the oxygenates obtained in step (e), other oxygenates may be providedto the oxygenate-to-olefin zone of step (f).

In step (d) of the process, olefins, preferably including ethylene, areproduced. Typically the olefins, together with any other compounds,leave the cracking zone as cracking zone effluent comprising olefins,including ethylene. Preferably, the ethylene is separated from theremainder of the cracking zone effluent, such as for instance hydrogenand propylene, prior to being used in any subsequent process. Theethylene may be separated using any suitable means in the art. Referenceis made to for instance US2005/0038304.

In step (f) of the process also olefins, preferably including ethylene,are produced. The olefins typically leave the OTO zone as part of an OTOzone effluent. As for the ethylene produced in step (d), it is preferredto separate the ethylene for the remainder to the OTO zone effluentprior to providing any of the ethylene to any subsequent process.

In the process according to the invention at least part of the crackingzone effluent and the OTO zone effluent are combined to form a combinedeffluent prior to separating of the ethylene. It has been foundadvantageous to combine at least part of the cracking zone effluent andthe OTO zone effluent to form a combined effluent. By separating theethylene from the combined effluent, rather than from the separateeffluents, efficient use can be made of the back-end facilities of theprocesses.

By combining the cracking zone effluent and the OTO zone effluent afurther advantage is obtained. In step (d) of the process, hydrogen isproduced in significant amounts. However, in step (f) of the processsome hydrogen is also produced. The OTO zone effluent therefore alsocomprises small amounts of hydrogen, typically in the range of from 0.05to 1 wt % based on the total hydrocarbon content in the OTO zoneeffluent. The amount of hydrogen in the OTO zone effluent, however, isrelatively small, making separating of the hydrogen from the remainderof the OTO zone effluent not worthwhile. By combining at least part ofthe cracking zone effluent and at least part of the OTO zone effluent toa combined effluent and subsequently separating hydrogen from thatcombined effluent it is possible to retrieve not only part or all of thehydrogen in the cracking zone effluent, but also at least part of thehydrogen in the OTO zone effluent. The hydrogen obtained from thecombined effluent is further also referred to a hydrogen ex. combinedeffluent. The hydrogen may be separated using any suitable means knownin the art, for example cryogenic distillation, pressure swingabsorption whereby hydrogen in the hydrogen containing stream absorbspreferentially over the impurities or via hydrogen permeable membrane.By combining the effluents of the cracking zone and the OTO zone, thehydrogen in the OTO zone effluent is also retrieved. Thereby, the amountof hydrogen available to add to the field carbon dioxide and synthesisgas provided to the oxygenate synthesis zone to synthesise oxygenates isincreased. Consequently, more field carbon dioxide can be provided tothe oxygenate synthesis zone and thus more carbon dioxide is captured inthe from of methanol, ethylene and other products.

At least part of the hydrogen obtained from the combined effluent isprovided to the oxygenate synthesis zone of step e) and is convertedwith at least field carbon dioxide and synthesis gas to oxygenates inthe oxygenate synthesis zone. This has the advantage that even morefield carbon dioxide can be captured. The hydrogen obtained from thecombined effluent does not contain carbon monoxide or carbon dioxide andtherefore can be fully utilised to react with field carbon dioxide.

As mentioned hereinabove it is preferred to use both carbon dioxide andcarbon monoxide to synthesise the oxygenates, while it is also preferredto combine the carbon dioxide ex. field with a synthesis that is rich inhydrogen. By providing at least part of the hydrogen obtained from thecombined effluent the molar ratio of the hydrogen, carbon dioxide andoptionally carbon monoxide provided to the oxygenate synthesis zone ofstep e) can be increased. It is particularly preferred in a process,wherein the synthesis gas produced in step (c) is hydrogen deficient, inparticular a synthesis gas having a molar ratio of hydrogen, carbondioxide and optionally carbon monoxide in the range of from 1.0 to 1.9,more preferably of from 1.3 to 1.8, wherein the molar ratio is definedhereinabove. Such a synthesis gas is typically produced with little oreven no steam added to the process. As a result the water consumption ofthe synthesis gas process is reduced, and thus the water consumption ofthe integrated process is reduced.

The synthesis gas is combined with hydrogen, for example obtained fromthe combined effluent. For example, a synthesis gas comprising mainlyhydrogen and carbon monoxide at a molar ratio of 1.6, may be combinedwith hydrogen, for example obtained from step (d) of the processaccording to the invention to form a hydrogen-enriched synthesis gas,which can be mixed with at least part of the carbon dioxide ex. field.Preferably, sufficient field carbon dioxide is added to the synthesisgas to provide a carbon dioxide concentration in the range of from 0.1to 25 mol %, preferably 3 to 15 mol %, more preferably of from 4 to 10mol %, based on the total number of moles of hydrogen, carbon monoxideand carbon dioxide in the mixture.

As mentioned, preferably, a synthesis gas is used comprising little orno carbon dioxide. The carbon dioxide ex. field preferably compriseslittle or no inerts like Ar, or N₂. When using a synthesis gas withlittle or no carbon dioxide, more field carbon dioxide can be added andless inerts are introduced to the oxygenate synthesis zone. Less wastecarbon dioxide is thus produced, which would otherwise need to besequestrated or captured and stored.

By using hydrogen obtained from combined effluent to produce at leastpart of the oxygenate feed to the OTO zone, the hydrogen produced duringthe cracking step or OTO is no longer combusted as fuel in the ethanefurnace, but rather used to produce valuable oxygenates. This hydrogenis obtained as co-product and does not add additional carbon dioxide ontop of what is required for the main reaction product ethylene. Inaddition, the hydrogen obtained from the combined effluent does notcomprise significant amounts of inerts such as N₂, Ar or CH₄. Theseinerts may typically be present in the natural gas or purified oxygenprovided to produce synthesis gas for methanol production.

By combining at least part of the cracking zone effluent and at leastpart of the OTO zone effluent to a combined effluent, at least part ofany olefins other than ethylene obtained in step (d) and step (f) arealso combined in one stream. The cracker zone effluent obtained from thecracking zone of step (d) comprises predominantly ethylene, but may alsocomprise up to 2 wt % propylene, based on the total weight of theethylene in the cracking zone effluent. This amount of propylene is noteconomically recoverable, however by combining the olefins obtained fromthe cracking zone in step (d) and the olefins obtained from the OTO zonein step (f), i.e. combining at least part of the cracking zone effluentand at least part of the OTO zone effluent to a combined effluent, acombined effluent is obtained that comprises in the range of 10 to 40%of propylene, based on the total hydrocarbon content of the combinedeffluent. The high propylene content in the combined effluent is causedby the high propylene content in the OTO zone effluent. OTO processesproduce a mix of olefins, comprising in the range of from 5 to 80 wt %of ethylene and in the range of from 10 to 80 wt % of propylene, basedon the total hydrocarbon content of the OTO zone effluent. By combiningthe effluent of the cracking zone and the OTO zone, it is possible toalso economically recover the propylene in the cracking zone effluent.The propylene can be used as a feedstock to a polypropylene productionprocess, optionally after being treated to remove impurities.Polypropylene production processes are well known in the art.

Besides olefins and hydrogen, the OTO process also produces smallamounts of alkanes, in particular ethane, propane and butane. A furthersynergy of the integrated process can be obtained by providing anyethane present in the effluent of the OTO zone to the cracking zone. Theethane can then be cracked to ethylene and hydrogen in the crackingzone, thus providing additional ethylene and hydrogen. The hydrogen maysubsequently be used to synthesise oxygenates.

Part of the ethylene produced in the process according to the inventioncan be used as a feedstock for several other processes, including thesynthesis of ethylene oxide, mono-ethylene-glycol and styrene monomer.

It has now also been found that it is possible to integrate theproduction of these products into the process according to the inventionto obtain further synergy.

A further integration may be achieved by converting at least part of theethylene produced in step (d), step (f) or, preferably, both steps (d)and (f) with benzene into ethyl benzene and converting at least part ofthe ethyl benzene to styrene monomer and at least hydrogen.

Each of the mentioned conversion steps hereinabove are well known in theart. Any suitable process may be used. Ethyl benzene is typicallyproduced by reacting ethylene and benzene in the presence of an acidcatalyst. Reference is for example made to made to Kniel et al.,Ethylene, Keystone to the petrochemical industry, Marcel Dekker, Inc,New York, 1980, in particular section 3.4.1, page 24 to 25. While thestyrene is produced by the catalytic dehydrogenation of ethyl benzene inthe presence of a suitable catalyst, examples of suitable catalystsinclude but are not limited to dehydrogenation catalysts based on iron(III) oxide.

By integrating the process according to the invention with theproduction of styrene monomer, as described above, further hydrogen isproduced next to the desired products. Preferably, this hydrogen isseparated from the other reaction products. As mentioned hereinabove,additional hydrogen, for instance produced in step (d) of the process,can be used to provide additional hydrogen to the oxygenate synthesiszone. Also, the hydrogen obtained from the conversion of ethylene, viaethylbenzene, to styrene monomer may preferably be used as additionalhydrogen to the oxygenate synthesis zone.

By providing additional hydrogen obtained from the conversion ofethylene, via ethylbenzene, into styrene to synthesise oxygenates, morefield carbon dioxide can be provided to the oxygenate synthesis zone.

The produced styrene monomer may be used to produce polystyrene.

Carbon dioxide other than field carbon dioxide may also be provided tothe oxygenate synthesis zone, in particular in case the amount of carbondioxide ex. field is insufficient to satisfy the full carbon dioxidedemand of the oxygenate synthesis. As mentioned hereinabove someadditional carbon dioxide may for instance be comprised in synthesis gasprovided to the oxygenate synthesis as part of the feed containinghydrogen. Other suitable sources of carbon dioxide may include:

-   -   a source comprising carbon dioxide obtained from a carbon        dioxide-comprising flue gas stream, in particular a flue gas        obtained from the integrated process according to the invention        or optionally an oxygen purification unit or synthesis gas        production process. The oxidation of ethylene to ethylene oxide        requires large amounts of purified oxygen. Preferably, the flue        gas is first concentrated to increase the carbon dioxide        concentration.    -   a source comprising the flue gas obtained from an oxidative        de-coking of an ethane cracking furnace, typically one of the        ethane cracking furnaces used for producing olefins in step (d).        In case the oxidative de-coking of the furnace is done using        pure oxygen or pure oxygen diluted in carbon dioxide instead of        air, an essentially pure stream of carbon dioxide can be        produced, which is especially suitable to be used in the        synthesis of oxygenates. Although, it is required to first        produce pure oxygen, there is no need to post-treat the flue gas        in order to capture the carbon dioxide. Also the decoking to the        OTO catalyst during regeneration of the catalyst can be        performed in a similar way to provide a suitable carbon dioxide        comprising stream.

A particularly preferred source of carbon dioxide may be obtained byconverting ethylene to ethylene oxide or MEG. Ethylene oxide and MEG arevaluable products, whereby MEG has the further advantage that it isliquid and therefore can be stored and transported relatively easy.

In the process according to the invention at least part of obtainedethylene from the ethane cracking step (d) and/or the OTO step (f),preferably both steps (d) and (f) may be oxidised to ethylene oxide byproviding at least part of the ethylene with a feed containing oxygen toan ethylene oxidation zone, further referred to as EO zone.

Preferably, the ethylene oxide is further converted tomono-ethylene-glycol (MEG). MEG is a liquid and therefore can betransported and stored more conveniently than ethylene oxide.Preferably, the EO zone is part of a larger mono-ethylene-glycolsynthesis zone, i.e. a second oxygenate synthesis zone, further referredto as MEG zone. Preferably, the MEG zone then comprises a first sectioncomprising the EO zone and a second ethylene oxide hydrolysis section.The MEG is synthesised by providing the ethylene oxide with a feedcontaining water to the ethylene oxide hydrolysis zone and convertingthe ethylene oxide to MEG. Optionally, the ethylene oxide is firstreacted with carbon dioxide to from ethylene carbonate, which issubsequently hydrolysed to obtain MEG and carbon dioxide, referenceherein is made to for instance US2008139853, incorporated by reference.

A by-product of the ethylene oxide process is carbon dioxide. During thereaction of ethylene with oxygen to ethylene oxide, carbon dioxide isformed as part of the ethylene is fully oxidised to carbon dioxide. Thecarbon dioxide is typically obtained as part of an EO zone effluent,which also comprises ethylene oxide. This is waste carbon dioxide andneeds to be sequestered or otherwise captured and stored.

By providing part of the carbon dioxide obtained as part of an EO zoneeffluent to the oxygenate synthesis zone of step (e) the need tosequester or otherwise capture or store this waste carbon dioxide isreduced.

Preferably, the carbon dioxide is separated from the OE zone effluent toobtain a separate carbon dioxide comprising stream, further alsoreferred to a carbon dioxide ex. EO. Preferably, the EO zone effluent isfurther treated to convert the ethylene oxide into MEG in a MEG zone.From the MEG zone, a MEG zone effluent is obtained, comprising MEG andcarbon dioxide. Suitably, the carbon dioxide can be separated from theMEG zone effluent by cooling the MEG zone effluent to a temperaturebelow the boiling point of MEG, this carbon dioxide is also referred toas carbon dioxide ex. MEG. As no additional carbon dioxide is producedby converting ethylene oxide into MEG the carbon dioxide ex. MEG is thesame as the carbon dioxide ex. EO. By reusing the carbon dioxide tosynthesize oxygenates, the carbon dioxide penalty for producing EO isreduced. A further advantage is that the stream comprising carbondioxide obtained from the EO or MEG zone comprises predominantly carbondioxide. Preferably the stream comprises in the range of 80 to 100 mol %of carbon dioxide and steam, based on the total amount of moles in thestream. More preferably, the stream comprising carbon dioxide comprisesessentially only carbon dioxide and, optionally, steam. Such a stream isparticularly suitable to be used in an oxygenate synthesis process as itdoes not introduce significant amounts of inerts, e.g. CH₄, N₂ and Ar,to the oxygenate synthesis zone. Should, however, the stream comprisingcarbon dioxide comprise significant amounts of other, undesired,compounds, e.g. ethylene oxide, the stream is preferably treated toremove such compounds prior to being introduced into the oxygenatesynthesis zone. Another advantage of the integration with a MEGsynthesis is that next to MEG, minor amounts of other oxygenates mayproduced in the MEG zone by the process for producing MEG, such as forinstance di-ethylene-glycol. These oxygenates may suitably be separatedfrom the obtained MEG zone effluent and provided to the OTO zone as partof the oxygenate feed.

In the present invention an ethane-comprising feed is cracked in step(d) in a cracking zone under cracking conditions to produce at leastolefins and hydrogen.

Additionally, small amounts of propylene are formed. Other by-productsmay be formed such as butylene, butadiene, ethyne, propyne and benzene.The cracking process is performed at elevated temperatures, preferablyin the range of from 650 to 1000° C., more preferably from 750 to 950°C. Typically, the cracking is performed in the presence of water (steam)as a diluent. The ethane conversion is typically in the range of from 40to 75 mol %, based on the total number of moles of ethane provided tothe cracking zone. Preferably, the un-cracked ethane is recycled back tothe cracking zone. Ethane cracking processes are well known to theskilled person and need no further explanation. Reference is forinstance made to Kniel et al., Ethylene, Keystone to the petrochemicalindustry, Marcel Dekker, Inc, New York, 1980, in particular chapters 6and 7.

In the present invention an oxygenate feedstock is converted in step (f)in an oxygenate-to-olefins process, in which an oxygenate feedstock iscontacted in an OTO zone with an oxygenate conversion catalyst underoxygenate conversion conditions, to obtain a conversion effluentcomprising lower olefins. In the OTO zone, at least part of the feed isconverted into a product containing one or more olefins, preferablyincluding light olefins, in particular ethylene and/or propylene.

Examples of oxygenates that can be used in the oxygenate feedstock ofstep f) of the process include alcohols, such as methanol, ethanol,isopropanol, ethylene glycol, propylene glycol; ketones, such as acetoneand methylethylketone; aldehydes, such as formaldehyde, acetaldehyde andpropionaldehyde; ethers, such as dimethylether, diethylether,methylethylether, tetrahydrofuran and dioxane; epoxides such as ethyleneoxide and propylene oxide; and acids, such as acetic acid, propionicacid, formic acid and butyric acid. Further examples are dialkylcarbonates such as dimethyl carbonate or alkyl esters of carboxylicacids such as methyl formate. Of these examples, alcohols and ethers arepreferred.

Examples of preferred oxygenates include alcohols, such as methanol,ethanol, isopropanol, ethylene glycol, propylene glycol; and dialkylethers, such as dimethylether, diethylether, methylethylether. Cyclicethers such as tetrahydrofuran and dioxane, are also suitable.

The oxygenate used in the process according to the invention ispreferably an oxygenate which comprises at least one oxygen-bonded alkylgroup. The alkyl group preferably is a C1-C4 alkyl group, i.e. comprises1 to 4 carbon atoms; more preferably the alkyl group comprises 1 or 2carbon atoms and most preferably one carbon atom. The oxygenate cancomprise one or more of such oxygen-bonded C1-C4 alkyl groups.Preferably, the oxygenate comprises one or two oxygen-bonded C1-C4 alkylgroups.

More preferably an oxygenate is used having at least one C1 or C2 alkylgroup, still more preferably at least one C1 alkyl group.

Preferably the oxygenate is chosen from the group of alkanols anddialkyl ethers consisting of dimethylether, diethylether,methylethylether, methanol, ethanol, isopropanol, and mixtures thereof.

Most preferably the oxygenate is methanol or dimethylether, or a mixturethereof.

Preferably the oxygenate feedstock comprises at least 50 wt % ofoxygenate, in particular methanol and/or dimethylether, based on totalhydrocarbons, more preferably at least 80 wt %, most preferably at least90 wt %.

The oxygenate feedstock can be obtained from a prereactor, whichconverts methanol at least partially into dimethylether. In this way,water may be removed by distillation and so less water is present in theprocess of converting oxygenate to olefins, which has advantages for theprocess design and lowers the severity of hydrothermal conditions thecatalyst is exposed to.

The oxygenate feedstock can comprise an amount of diluents, such aswater or steam.

A variety of OTO processes are known for converting oxygenates such asfor instance methanol or dimethylether to an olefin-containing product,as already referred to above. One such process is described in WO-A2006/020083, incorporated herein by reference, in particular inparagraphs [0116]-[0135]. Processes integrating the production ofoxygenates from synthesis gas and their conversion to light olefins aredescribed in US2007/0203380A1 and US2007/0155999A1.

Catalysts as described in WO A 2006/020083 are suitable for convertingthe oxygenate feedstock in step (f) of the present invention. Suchcatalysts preferably include molecular sieve catalyst compositions.Suitable molecular sieves are silicoaluminophosphates (SAPO), such asSAPO-17, -18, -34, -35, -44, but also SAPO-5, -8, -11, -20, -31, -36,-37, -40, -41, -42, -47 and -56.

Alternatively, the conversion of the oxygenate feedstock may beaccomplished by the use of an aluminosilicate catalyst, in particular azeolite. Suitable catalysts include those containing a zeolite of theZSM group, in particular of the MFI type, such as ZSM-5, the MTT type,such as ZSM-23, the TON type, such as ZSM-22, the MEL type, such asZSM-11, the FER type. Other suitable zeolites are for example zeolitesof the STF-type, such as SSZ-35, the SFF type, such as SSZ-44 and theEU-2 type, such as ZSM-48. Aluminosilicate catalysts are preferred whenan olefinic co-feed is fed to the oxygenate conversion zone togetherwith oxygenate, for increased production of ethylene and propylene.

The reaction conditions of the oxygenate conversion include those thatare mentioned in WO-A 2006/020083. Hence, a reaction temperature of 200to 1000° C., preferably from 250 to 750° C., and a pressure from 0.1 kPa(1 mbar) to 5 MPa (50 bar), preferably from 100 kPa (1 bar) to 1.5 MPa(15 bar), are suitable reaction conditions.

A specially preferred OTO process for use in step (f) of the presentinvention will now be described. This process provides particularly highconversion of oxygenate feed and a recycle co-feed to ethylene andpropylene. Reference is made in this regard also to WO2007/135052,WO2009/065848, WO2009/065875, WO2009/065870, WO2009/065855,WO2009/065877, in which processes a catalyst comprising analuminosilicate or zeolite having one-dimensional 10-membered ringchannels, and an olefinic co-feed and/or recycle feed is employed.

In this process, the oxygenate-conversion catalyst comprises one or morezeolites having one-dimensional 10-membered ring channels, which are notintersected by other channels, preferably at least 50% wt of suchzeolites based on total zeolites in the catalyst. Preferred examples arezeolites of the MTT and/or TON type. In a particularly preferredembodiment the catalyst comprises in addition to one or moreone-dimensional zeolites having 10-membered ring channels, such as ofthe MTT and/or TON type, a more-dimensional zeolite, in particular ofthe MFI type, more in particular ZSM-5, or of the MEL type, such aszeolite ZSM-11. Such further zeolite (molecular sieve) can have abeneficial effect on the stability of the catalyst in the course of theOTO process and under hydrothermal conditions. The second molecularsieve having more-dimensional channels has intersecting channels in atleast two directions. So, for example, the channel structure is formedof substantially parallel channels in a first direction, andsubstantially parallel channels in a second direction, wherein channelsin the first and second directions intersect. Intersections with afurther channel type are also possible. Preferably the channels in atleast one of the directions are 10-membered ring channels. A preferredMFI-type zeolite has a Silica-to-Alumina ratio SAR of at least 60,preferably at least 80, more preferably at least 100, even morepreferably at least 150. The oxygenate conversion catalyst can compriseat least 1 wt %, based on total molecular sieve in the oxygenateconversion catalyst, of the second molecular sieve havingmore-dimensional channels, preferably at least 5 wt %, more preferablyat least 8 wt %, and furthermore can comprise less than 35 wt % of thefurther molecular sieve, in certain embodiments less than 20 wt %, orless than 18 wt %, such as less than 15 wt %.

Especially when the oxygenate conversion is carried out over a catalystcontaining MTT or TON type aluminosilicates, it may be advantageous toadd an olefin-containing co-feed together with the oxygenate feed (suchas dimethylether-rich or methanol-rich) feed to the OTO zone when thelatter feed is introduced into this zone. It has been found that thecatalytic conversion of the oxygenates, in particular methanol and DME,to ethylene and propylene is enhanced when an olefin is present in thecontact between methanol and/or dimethylether and the catalyst.Therefore, suitably, an olefinic co-feed is added to the reaction zonetogether with the oxygenate feedstock.

In special embodiments, at least 70 wt % of the olefinic co-feed, duringnormal operation, is formed by a recycle stream of a C3+ or C4+ olefinicfraction from the OTO conversion effluent, preferably at least 90 wt %,more preferably at least 99 wt %, and most preferably the olefinicco-feed is during normal operation formed by such recycle stream. In oneembodiment the olefinic co-feed can comprise at least 50 wt % of C4olefins, and at least a total of 70 wt % of C4 hydrocarbon species. Itcan also comprise propylene. The OTO conversion effluent can comprise 10wt % or less, preferably 5 wt % or less, more preferably 1 wt % or less,of C6-C8 aromatics, based on total hydrocarbons in the effluent. Atleast one of the olefinic co-feed, and the recycle stream, can inparticular comprise less than 20 wt % of C5+ olefins, preferably lessthan 10 wt % of C5+ olefins, based on total hydrocarbons in the olefinicco-feed.

In order to maximize production of ethylene and propylene, it isdesirable to maximize the recycle of C4 olefins. In a stand-aloneprocess, i.e. without integration with a cracker, there is a limit tothe maximum recycle of a C4 fraction from the OTO effluent. A certainpart thereof, such as between 1 and 5 wt %, needs to be withdrawn aspurge, since otherwise saturated C4's (butane) would build up which aresubstantially not converted under the OTO reaction conditions.

In the preferred process, optimum light olefins yield are obtained whenthe OTO conversion is conducted at a temperature of more than 450° C.,preferably at a temperature of 460° C. or higher, more preferably at atemperature of 480° C. or higher, in particular at 500° C. or higher,more in particular 550° C. or higher, or 570° C. or higher. Thetemperature will typically less than 700° C., or less than 650° C. Thepressure will typically be between 0.5 and 15 bar, in particular between1 and 5 bar.

In a special embodiment, the oxygenate conversion catalyst comprisesmore than 50 wt %, preferably at least 65 wt %, based on total molecularsieve in the oxygenate conversion catalyst, of the one-dimensionalmolecular sieve having 10-membered ring channels.

In one embodiment, molecular sieves in the hydrogen form are used in theoxygenate conversion catalyst, e.g., HZSM-22, HZSM-23, and HZSM-48,HZSM-5. Preferably at least 50% w/w, more preferably at least 90% w/w,still more preferably at least 95% w/w and most preferably 100% of thetotal amount of molecular sieve used is in the hydrogen form. When themolecular sieves are prepared in the presence of organic cations themolecular sieve may be activated by heating in an inert or oxidativeatmosphere to remove organic cations, for example, by heating at atemperature over 500° C. for 1 hour or more. The zeolite is typicallyobtained in the sodium or potassium form. The hydrogen form can then beobtained by an ion exchange procedure with ammonium salts followed byanother heat treatment, for example in an inert or oxidative atmosphereat a temperature over 500° C. for 1 hour or more. The molecular sievesobtained after ion-exchange are also referred to as being in theammonium form.

The molecular sieve can be used as such or in a formulation, such as ina mixture or combination with a so-called binder material and/or afiller material, and optionally also with an active matrix component.Other components can also be present in the formulation. If one or moremolecular sieves are used as such, in particular when no binder, filler,or active matrix material is used, the molecular sieve itself is/arereferred to as oxygenate conversion catalyst. In a formulation, themolecular sieve in combination with the other components of the mixturesuch as binder and/or filler material is/are referred to as oxygenateconversion catalyst.

It is desirable to provide a catalyst having good mechanical or crushstrength, because in an industrial environment the catalyst is oftensubjected to rough handling, which tends to break down the catalyst intopowder-like material. The latter causes problems in the processing.Preferably the molecular sieve is therefore incorporated in a bindermaterial. Examples of suitable materials in a formulation include activeand inactive materials and synthetic or naturally occurring zeolites aswell as inorganic materials such as clays, silica, alumina,silica-alumina, titania, zirconia and aluminosilicate. For presentpurposes, inactive materials of a low acidity, such as silica, arepreferred because they may prevent unwanted side reactions which maytake place in case a more acidic material, such as alumina orsilica-alumina is used.

Typically the oxygenate conversion catalyst deactivates in the course ofthe process. Conventional catalyst regeneration techniques can beemployed. The catalyst particles used in the process of the presentinvention can have any shape known to the skilled person to be suitablefor this purpose, for it can be present in the form of spray driedcatalyst particles, spheres, tablets, rings, extrudates, etc. Extrudedcatalysts can be applied in various shapes, such as, cylinders andtrilobes. If desired, spent oxygenate conversion catalyst can beregenerated and recycled to the process of the invention. Spray-driedparticles allowing use in a fluidized bed or riser reactor system arepreferred. Spherical particles are normally obtained by spray drying.Preferably the average particle size is in the range of 1-200 μm,preferably 50-100 μm.

The preferred embodiment of step (f) described hereinabove is preferablyperformed in an OTO zone comprising a fluidized bed or moving bed, e.g.a fast fluidized bed or a riser reactor system, although in general foran OTO process, in particular for an MTP process, also a fixed bedreactor or a tubular reactor can be used. Serial reactor systems can beemployed.

In one embodiment, the OTO zone comprises a plurality of sequentialreaction sections. Oxygenate can be added to at least two of thesequential reaction sections.

When multiple reaction zones are employed, an olefinic co-feed isadvantageously added to the part of the dimethylether-rich feed that ispassed to the first reaction zone.

The preferred molar ratio of oxygenate in the oxygenate feedstock toolefin in the olefinic co-feed provided to the OTO conversion zonedepends on the specific oxygenate used and the number of reactiveoxygen-bonded alkyl groups therein. Preferably the molar ratio ofoxygenate to olefin in the total feed lies in the range of 20:1 to 1:10,more preferably in the range of 18:1 to 1:5 and still more preferably inthe range of 15:1 to 1:3.

A diluent can also be fed to the OTO zone, mixed with the oxygenateand/or co-feed if present, or separately. A preferred diluent is steam,although other inert diluents can be used as well. In one embodiment,the molar ratio of oxygenate to diluent is between 10:1 and 1:10,preferably between 4:1 and 1:2, most preferably between 3:1 and 1:1,such as 1.5:1, in particular when the oxygenate is methanol and thediluent is water (steam).

The feedstock comprising methane, ethane and carbon dioxide may be anyfeedstock comprising methane, ethane and carbon dioxide. Preferably, thefeedstock is natural gas or associated gas. Reference herein toassociated gas is to C1 to C5 hydrocarbons co-produced with theproduction of oil. Preferably the feedstock comprises in the range offrom 0.1 to 70 mol % of carbon dioxide, more preferably from 0.5 to 35mol %, even more preferably from 1 to 30 mol %, based on the totalcontent of the feedstock. The feedstock comprising methane, ethane andcarbon dioxide may further comprise higher hydrocarbons, including butnot limited to, propane, butanes and pentanes.

Preferably, the feed comprising methane and ethane comprises in therange of from 1 to 20 mol % of ethane, based on the total feed.

The methane-comprising feed, preferably, comprises in the range of from50 to 100 mol % of methane, more preferably 80 to 99 mol % of methane,based on the total number of moles in the methane-comprising feed.

The ethane-comprising feed, preferably, comprises in the range of from50 to 100 mol % of ethane, more preferably 80 to 99 mol % of ethane,based on the total number of moles in the ethane-comprising feed.

The carbon dioxide-comprising feed (or carbon dioxide ex. field),preferably, comprises in the range of from 90 to 100 mol % of carbondioxide, more preferably 97 to 99 mol % of carbon dioxide, based on thetotal number of moles in the carbon dioxide-comprising feed.

The oxygenates provided to step (f) of the process according to theinvention may be any oxygenates preferably methanol and/or DME. Theoxygenate feedstock comprises at least oxygenates obtained in step (e).The oxygenates may further comprise oxygenates, such as for exampleother alcohols, other ethers, aldehydes, ketones and esters. Preferably,the oxygenates are provided together with water as a diluent. Anoxygenate feedstock provided to the process may also comprise compoundsother than water and oxygenates.

In one embodiment, the oxygenate is obtained as a reaction product ofsynthesis gas. Synthesis gas can for example be generated from fossilfuels, such as from natural gas or oil, or from the gasification ofcoal. Suitable processes for this purpose are for example discussed inIndustrial Organic Chemistry, Klaus Weissermehl and Hans-Jürgen Arpe,3rd edition, Wiley, 1997, pages 13-28. This book also describes themanufacture of methanol from synthesis gas on pages 28-30.

In another embodiment the oxygenate is obtained from biomaterials, suchas through fermentation. For example by a process as described inDE-A-10043644.

Preferably, at least part of the oxygenate feed is obtained byconverting methane into synthesis gas and providing the synthesis gas toa oxygenate synthesis zone to synthesise oxygenates. The methane ispreferably obtained from natural gas or associated gas, more preferablythe same natural gas or associated gas, from which the light paraffinfeedstock for the cracker is obtained.

The oxygenates may be provided directly from one or more oxygenatesynthesis zones, however, it may also be provided from a centraloxygenate storage facility.

The olefinic co-feed optionally provided together with the oxygenatefeedstock to the OTO conversion zone may contain one olefin or a mixtureof olefins. Apart from olefins, the olefinic co-feed may contain otherhydrocarbon compounds, such as for example paraffinic, alkylaromatic,aromatic compounds or a mixture thereof. Preferably the olefinic co-feedcomprises an olefinic fraction of more than 20 wt %, more preferablymore than 25 wt %, still more preferably more than 50 wt %, whicholefinic fraction consists of olefin(s). The olefinic co-feed canconsist essentially of olefin(s).

Any non-olefinic compounds in the olefinic co-feed are preferablyparaffinic compounds. If the olefinic co-feed contains any non-olefinichydrocarbon, these are preferably paraffinic compounds. Such paraffiniccompounds are preferably present in an amount in the range from 0 to 80wt %, more preferably in the range from 0 to 75 wt %, still morepreferably in the range from 0 to 50 wt %.

By an unsaturate is understood an organic compound containing at leasttwo carbon atoms connected by a double or triple bond. By an olefin isunderstood an organic compound containing at least two carbon atomsconnected by a double bond. The olefin can be a mono-olefin, having onedouble bond, or a poly-olefin, having two or more double bonds.Preferably olefins present in an olefinic co-feed are mono-olefins. C4olefins, also referred to as butenes (1-butene, 2-butene, iso-butene,and/or butadiene), in particular C4 mono-olefins, are preferredcomponents in the olefinic co-feed.

Preferred olefins have in the range from 2 to 12, preferably in therange from 3 to 10, and more preferably in the range from 4 to 8 carbonatoms.

Examples of suitable olefins that may be contained in the olefinicco-feed include ethene, propene, butene (one or more of 1-butene,2-butene, and/or iso-butene (2-methyl-1-propene)), pentene (one or moreof 1-pentene, 2-pentene, 2-methyl-1-butene, 2-methyl-2-butene,3-methyl-1-butene, and/or cyclopentene), hexene (one or more of1-hexene, 2-hexene, 3-hexene, 2-methyl-1-pentene, 2-methyl-2-pentene,3-methyl-1-pentene, 3-methyl-2-pentene, 4-methyl-1-pentene,4-methyl-2-pentene, 2,3-dimethyl-1-butene, 2,3-dimethyl-2-butene,3,3-dimethyl-1-butene, methylcyclopentene and/or cyclohexene), heptenes,octenes, nonenes and decenes. The preference for specific olefins in theolefinic co-feed may depend on the purpose of the process, such aspreferred production of ethylene or propylene.

In a preferred embodiment the olefinic co-feed preferably containsolefins having 4 or more carbon atoms (i.e. C₄+ olefins), such asbutenes, pentenes, hexenes and heptenes. More preferably the olefinicfraction of the olefinic co-feed comprises at least 50 wt % of butenesand/or pentenes, even more preferably at least 50% wt of butenes, andmost preferably at least 90 wt % of butenes. The butene may be 1-, 2-,or iso-butene, or a mixture of two or more thereof.

Preferably, at least part of the oxygenate feed is obtained byconverting methane into synthesis gas and providing the synthesis gas toa oxygenate synthesis zone to synthesise oxygenates. The methane ispreferably obtained from natural gas or associated gas, more preferablythe same natural gas or associated gas, from which the ethane-comprisingfeed was obtained.

The benzene used to convert ethylene into ethyl benzene may be anybenzene available. The benzene may be benzene produced in step (a) ofthe process according to the invention. As disclosed in U.S. Pat. No.6,677,496, ethane cracking processes typically produce up to 0.6 wt % ofbenzene, based on the total ethane feed. However, the benzene may alsobe obtained from any other source.

Preferably, the benzene is produced from higher hydrocarbons such aspropane and butane, more preferably propane and butane obtained ascondensate or LPG from the natural gas or associated gas which served asthe feedstock comprising methane, ethane and carbon dioxide.

In another aspect, the invention provides an integrated system forproducing olefins, which system comprises:

-   -   a) a separation system, having at least an inlet for a feed        comprising methane, ethane and carbon dioxide, and an outlet for        a methane-comprising feed, an outlet for an ethane-comprising        feed and an outlet for a carbon dioxide-comprising feed;    -   b) a partial oxidation system arranged to partially oxidise the        methane-comprising feed to a synthesis gas, having an inlet for        a methane-comprising feed to receive the methane-comprising feed        from the separation system, an inlet for oxygen, and an outlet        for synthesis gas;    -   c) a steam cracking system having one or more inlets for an        ethane-comprising feed to receive the methane-comprising feed        from the separation system and an inlet for steam, and an outlet        for a cracker effluent comprising olefins;    -   d) an oxygenate-to-olefins conversion system, having one or more        inlets for receiving an oxygenate feedstock, and comprising a        reaction zone for contacting the oxygenate feedstock with an        oxygenate conversion catalyst under oxygenate conversion        conditions, and an outlet for an oxygenate-to-olefins effluent        comprising olefins, including at least ethylene;    -   e) a work-up system arranged to receive at least part of the        cracker effluent and at least part of the oxygenate-to-olefins        effluent to obtain a combined effluent, the work-up section        comprising a separation system, an outlet for ethylene and an        outlet for hydrogen;    -   f) an oxygenate synthesis system having one or more inlets for        synthesis gas to receive the synthesis gas from the partial        oxidation system, an inlet for hydrogen and an inlet for a        carbon dioxide-comprising feed to receive the carbon        dioxide-comprising feed from the separation system, and an        outlet for an oxygenate feedstock; and        means for providing the oxygenate feedstock from the outlet for        oxygenate feedstock of the oxygenate synthesis system to the        oxygenate feedstock inlet of the oxygenate-to-olefins conversion        system and means for providing hydrogen from the outlet for        hydrogen of the work-up section to the inlet for hydrogen of the        oxygenate synthesis system.

The inlet for hydrogen of the oxygenate synthesis system may be the sameas the inlet for synthesis gas.

In FIG. 1, a schematic representation is given of an embodiment ofintegrated system for producing olefins according to the invention. Inthe system of FIG. 1, a ethane-comprising feed and steam are providedvia conduits 1 and 3 respectively to steam cracking system 5, comprisinga cracking zone for steam cracking ethane to ethylene. From steamcracking system 5, a cracking zone effluent is retrieved via conduit 7.

In FIG. 1, also a synthesis gas and a carbon dioxide-comprising areprovided via conduits 9 and 10, respectively, to oxygenate synthesissystem 11, comprising an oxygenate synthesis zone for synthesizingoxygenates from hydrogen and at least one of carbon monoxide and carbondioxide. From oxygenate synthesis system 11, an oxygenate feedstock isretrieved via conduit 13. The oxygenate feedstock is provided tooxygenate-to-olefins conversion system 15, comprising an OTO zone forconverting oxygenates to lower olefins, e.g. ethylene and propylene.Optionally, an olefinic co-feed (not shown) is provided tooxygenate-to-olefins conversion system 15 together with the oxygenatefeedstock. From oxygenate-to-olefins conversion system 13, an OTO zoneeffluent is retrieved via conduit 17.

The cracking zone effluent and the OTO zone effluent are combined toform combined effluent in conduit 19 and provided to work-up section 21.Work-up section 21 comprises at least a separation system to separateethylene from the combined effluent. In addition, hydrogen is separatedfrom the combined effluent and provided to oxygenate synthesis system 11via conduit 23. The ethylene is retrieved separately from workup section21 and provided via conduit 25 to ethylene oxidation system 27, whichcomprises an oxygenation zone for oxidising ethylene to ethylene oxide.Oxygen is provided to ethylene oxidation system 27 via conduit 29. Fromethylene oxide system 27, ethylene oxide is retrieved via conduit 31 andprovided to ethylene oxide hydrolysis system 33, which comprises anethylene oxide hydrolysis zone, wherein ethylene oxide is hydrolysed toMEG. Water is provided to ethylene oxide hydrolysis system 33 viaconduit 35. Ethylene oxidation system 27 and ethylene oxide hydrolysissystem 33 are comprised in MEG synthesis system 37. From MEG synthesissystem 37, a MEG-comprising effluent is retrieved via conduit 39 andcarbon dioxide via conduit 41. In FIG. 1, a feed comprising methane,ethane and carbon dioxide is provided via conduit 101 to separationsystem 103. In separation system 103, the feed comprising methane,ethane and carbon dioxide is separated into at least amethane-comprising feed, an ethane-comprising feed and a carbondioxide-comprising feed. From separation system 103, the ethanecomprising feed is provided via conduit 1 to steam cracking system 5.The methane-comprising feed is provided via conduit 107 to partialoxidation system 109 to be partially oxidised to form synthesis gas.Oxygen is provided via conduit 111 to partial oxidation system 109. Frompartial oxidation system 109, the synthesis gas is retrieved via conduit9 and provided to oxygenate synthesis system 11. The carbondioxide-comprising feed is provided from separation system 103 tooxygenate synthesis system 11 via conduit 10.

EXAMPLES

The invention is illustrated by the following non-limiting calculatedexamples.

Example 1

In the Examples, several options of implementing the present inventionare compared with comparative examples, by means of model calculations.As basis for Examples 1a to g, a model integrated OTO/ethane crackerprocess was taken. In Table 1, an overview is provided of the feed inputand the calculated products.

Calculations were done using a Spyro based model for modelling ofcracker operation combined with a proprietary model for modelling theOTO conversion. The key input to the models was as follows:

Cracking:

Steam to ethane ratio is 0.35 wt %. USC coil is used for the Spyrocalculations. Calculated at a coil outlet pressure of 1.77 bar absolute,at 65% ethane conversion and a residence time of 0.24 seconds.

OTO Conversion:

MeOH 5012 t/d is fed to the OTO reactor together with 1384 t/d ofrecycled and superheated steam and 1775 t/d of recycled C4 stream. Themodel was calibrated on small-scale experiments conducted to determineproduct distributions for single-pass OTO conversions. Therein, allcomponents that were fed to the OTO reactor have been evaporated andheated such that the temperature in the reactor is controlled between550-600° C. The pressure in the reactor is 2 bar absolute. The OTOcatalyst is fluidized in the reaction medium under the condition thatthe weight hourly space velocity (WHSV) is 4-10 h⁻¹, whereby WHSV isdefined as the total weight of the feed flow over the catalyst weightper hour. The following catalyst was used: Composition and preparation:32 wt % ZSM-23 SAR 46, 8 wt % ZSM-5 SAR 280, 36 wt % kaolin, 24 wt %silica sol, and, after calcination of the ammonium form of the spraydried particle, 1.5 wt % P was introduced by H₃PO₄ impregnation. Thecatalyst was again calcined at 550° C. The steam and C4 recycle streamsare excluded from the product composition tables.

The methanol provided to the OTO process (approximately 5000 t/d, seeTable 1) is synthesised using at least part of the field carbon dioxide.

As feedstock comprising methane, ethane and carbon dioxide, a naturalgas was used having the following composition: 89.8 mol % CH₄, 5.4 mol %C₂H₆, 4.4 mol % N₂, 0.4 mol % CO₂, and 0.1 mol % Ar, based on the totalnumber of moles in the natural gas stream.

The ethane-comprising feed is obtained by separating the ethane from thenatural gas. The remainder of the natural gas is used as themethane-comprising feed. The composition of the methane-comprising feedis: 94.3 mol % CH₄, 0.6 mol % C₂H₆, 4.6 mol % N₂, 0.4 mol % CO₂, and 0.1mol % Ar, based on the total number of moles in the methane-comprisingfeed.

Additional carbon dioxide is added to simulate a carbon dioxide streamseparated from the natural gas.

Optionally, additional hydrogen obtained from the combined effluent isadded.

Both hydrogen ex. combined effluent and carbon dioxide ex. field aretaken as 99.9+% pure.

The yields of methanol are calculated by an Aspen model. To keep theinert concentration of about 40 wt % in the synthesis gas recycle, theamount of purge stream from the recycle is adjusted.

The methane-comprising feed is converted to synthesis gas usingdifferent processes resulting in the following synthesis gasses:

Synthesis gas from a non-catalytic partial oxidation of natural gas(Shell gasification process). The SGP syngas comprises 61.2 mol %hydrogen, 34.0 mol % carbon monoxide, 2.1 mol % carbon dioxide and 2.5mol % inerts (N₂, Ar and CH₄), based on the total number of moles in theSGP syngas.

Synthesis gas from an auto-thermal reforming of natural gas (ATR). TheATR syngas comprises 65.5 mol % hydrogen, 26.7 mol % carbon monoxide,6.4 mol % carbon dioxide and 1.7 mol % inerts (N₂, Ar and CH₄), based onthe total number of moles in the ATR syngas.

A mixture of synthesis gas from a steam methane reforming (SMR) and aSGP synthesis gas. The mixture comprises 65.8 mol % hydrogen, 25.6 mol %carbon monoxide, 4.4 mol % carbon dioxide and 3.8 mol % inerts (N₂, Arand CH₄), based on the total number of moles in the mixture of syngas.

Table 2a provides an overview of the feed, i.e. carbon dioxide ex.field, synthesis gas and hydrogen ex. combined effluent, provided to themethanol synthesis.

Table 2b provides an overview of the feed composition provided to themethanol synthesis.

Table 3 provides an overview of the feedstock, i.e. methane-comprisingfeed, oxygen and water, required to produce the synthesis gas.

Table 4 shows the methanol production based on field carbon dioxide.

Experiment 1a: (not According to the Invention)

The methanol feed to the OTO process is synthesised from a mixture ofSGP and SMR synthesis gas. 2949 ton/day of natural gas is required toproduce sufficient methanol.

Experiment 1b: (not According to the Invention)

The methanol feed to the OTO process is synthesised from a mixture ofpart of the hydrogen ex. combined effluent and SGP synthesis gas. 2722ton/day of methane-comprising feed is required to produce sufficientmethanol.

Furthermore, inert (N₂, Ar and CH₄) concentrations in the feed to themethanol synthesis are reduced, compared to the levels seen inexperiment 1a, due to dilution of the SGP synthesis gas with hydrogenobtained from the ethane cracker.

Experiment 1c:

The methanol feed to the OTO process is synthesised from a mixture ofcarbon dioxide ex. field, hydrogen ex. combined effluent and SGPsynthesis gas. By addition of field carbon dioxide, the carbon dioxidecontent is increased to 3.3 mol %, based on the total feed to themethanol synthesis. The methane-comprising feed consumption forproducing the methanol has decreased by 12 wt % and 5 wt % respectivelybased on the methane-comprising feed required for producing the methanolin Experiments 1a and 1b. In addition, 255 ton/day of methanol isproduced based on field carbon dioxide, i.e. not produced as part of theprocess to prepare synthesis gas, which would need to be sequestered orotherwise captured and stored. As a result, the carbon dioxide penaltyof the process is reduced.

Again, inert (N₂, Ar and CH₄) concentrations are further lowered.

Experiment 1d:

The methanol feed to the OTO process is synthesised from a mixture ofcarbon dioxide ex. field, hydrogen ex. combined effluent, SGP synthesisgas and the addition of additional hydrogen for instance from a secondor further ethane cracker unit, or styrene production unit. By additionof field carbon dioxide, the carbon dioxide content is increased to 7.9mol %, based on the total feed to the methanol synthesis. Themethane-comprising feed consumption for producing the methanol hasdecreased by 27 wt % and 21 wt % respectively based on themethane-comprising feed required for producing the methanol inExperiments 1a and 1b. In addition 1062 ton/day of methanol is producedbased on field carbon dioxide.

Again, inert (N₂, Ar and CH₄) concentrations are further lowered.

Experiment 1e: (not According to the Invention)

The methanol feed to the OTO process is synthesised from a mixture ofpart of the hydrogen ex. combined effluent and ATR synthesis gas. 2933ton/day of methane-comprising feed is required to produce sufficientmethanol.

Experiment 1f:

The methanol feed to the OTO process is synthesised from a mixture ofcarbon dioxide ex. field, hydrogen ex. combined effluent and ATRsynthesis gas. By addition of field carbon dioxide, the carbon dioxidecontent is increased to 7.1 mol %, based on the total feed to themethanol synthesis. The methane-comprising feed consumption forproducing the methanol has decreased by 6 wt % and 5 wt % respectivelybased on the methane-comprising feed required for producing the methanolin Experiments 1a and 1e. In addition 273 ton/day of methanol isproduced based on field carbon dioxide. As a result, the carbon dioxidepenalty of the process is reduced.

Again, inert (N₂, Ar and CH₄) concentrations are further lowered.

Experiment 1g:

The methanol feed to the OTO process is synthesised from a mixture ofcarbon dioxide ex. field, hydrogen ex. cracker and ATR synthesis gas. Byaddition of field carbon dioxide from the MEG production unit the carbondioxide content is increased to 7.9 mol %, based on the total feed tothe methanol synthesis. The methane-comprising feed gas consumption forproducing the methanol has decreased by 9 wt % and 8.9 wt % respectivelybased on the methane-comprising feed required for producing the methanolin Experiments 1a and 1e. In addition, 443 ton/day of methanol isproduced based on field carbon dioxide. As a result, the carbon dioxidepenalty of the process is reduced.

Again, inert (N₂, Ar and CH₄) concentrations are further lowered.

TABLE 1 Ethane Integrated OTO/ethane OTO cracker cracker 10³ kg/day 10³kg/day 10³ kg/day Feed: Methanol 5012 5012 Ethane 2755 2755 Products:Ethylene 512 2187 2713 Propylene 1275 50 1325 Ethane 17 propane 48 19 67 >C3 318 135  453 Fuel gas 98 197  280 H₂O 2710 −83 2627 Hydrogen 17168   186** *based on CH₂ in the feed **including hydrogen obtained byrecycling ethane in the effluent of the OTO to the ethane cracker.

TABLE 2A Feed 10³ kg/day H₂ ex. Product combined 10³ kg/day Exp.effluent Synthesis gas CO₂ ex MEG Methanol 1a — 2236 (ex. SMR) — 50003883 (ex. SGP) 1b 129 5488 (ex. SGP) — 5000 1c 173 5208 (ex. SGP) 3655000 1d 321 4322 (ex. SGP) 1584  5000 1e  82 5837 (ex. ATR) — 5000 1f134 5518 (ex. ATR) 398 5000 1g 165 5320 (ex. ATR) 635 5000

TABLE 2b Composition mol %* Exp. H₂ CO CO₂ N₂, AR, CH₄ H₂O Molar ratio1a 65.8 25.6 4.4 3.8 0.2 2.05 1b 66.1 29.7 1.8 2.2 0.2 2.04 1c 66.7 27.83.3 2.0 0.2 2.04 1d 68.5 21.8 8.0 1.6 0.1 2.03 1e 68.1 24.6 5.9 1.4 >0.12.04 1f 68.6 22.9 7.2 1.3 >0.1 2.04 1g 69.0 21.9 7.9 1.2 >0.1 2.05*Based on the total number of moles in the feed **molar ratio = (#mol H₂− #mol CO₂)/(#mol CO + #mol CO₂)

TABLE 3 Feed Total 10³ kg/day feedstock Exp. methane-comprising feed O₂H₂O 10³ kg/day 1a 2949 2291 1210 6450 1b 2722 3239   0* 5961 1c 25833074   0* 5657 1d 2144 2551   0* 4695 1e 2933 3109 1691 7733 1f 27732939 1599 7311 1g 2674 2834 1541 7049 *In principle no water is added.

TABLE 4 Feed Product 10³ kg/day 10³ kg/day Exp. CO₂ ex field MethanolMethanol from field CO₂ 1a — 5000 1b — 5000 1c 365 5000 255 1d 1584 5000 1062 1e — 5000 1f 398 5000 273 1g 635 5000 443

By using a synthesis gas such as SGP synthesis gas, which comprisesrelatively low amounts of carbon dioxide it is possible to capturesignificant amounts of field carbon dioxide in the form of methanol,ethylene, MEG or products derived therefrom. In addition, by using asynthesis gas which is produced by a process in which in principle no oronly little water is used, such as a non-catalytic partial oxidationprocess, water consumption is significantly lowered. By using hydrogenex. Combined effluent for the production of methanol, additional amountsof field carbon dioxide can be captured in the form of methanol,ethylene, MEG or products derived thereof.

What is claimed is:
 1. A process for producing olefins, comprising: a.providing a feed comprising at least methane, ethane and carbon dioxide;b. separating the feed into at least a methane-comprising feed, anethane-comprising feed and a carbon dioxide-comprising feed; c.providing at least part of the methane-comprising feed to a process forpreparing synthesis gas to obtain a synthesis gas; d. cracking theethane-comprising feed in a cracking zone under cracking conditions toobtain a cracking zone effluent comprising at least olefins andhydrogen; e. providing at least part of the carbon dioxide-comprisingfeed and at least part the synthesis gas obtained in step c) to anoxygenate synthesis zone and synthesising oxygenates; f. converting atleast part of the oxygenates obtained in step (e) in anoxygenate-to-olefin zone to obtain an oxygenate-to-olefin zone effluentcomprising at least olefins and hydrogen; g. combining at least part ofthe cracking zone effluent and at least part of the OTO zone effluent toobtain a combined effluent; h. separating hydrogen from the combinedeffluent and providing at least part of the hydrogen to the oxygenatesynthesis zone in step (e).
 2. A process according to claim 1,comprising providing carbon dioxide, synthesis gas, and hydrogen to theoxygenate synthesis zone in a amount such that the molar ratio ofhydrogen, carbon monoxide and carbon dioxide provided to the oxygenatesynthesis zone is in the range of from 2.0 to 3.0.
 3. A processaccording to claim 2, wherein carbon dioxide is present in aconcentration in the range of from 0.1 to 25 mol %, based on the totalnumber of moles of carbon dioxide, hydrogen, and carbon monoxide.
 4. Aprocess according to claim 1, wherein the olefins obtained in step (d)and/or (f) include ethylene, the process further comprising: providingat least part of the ethylene to an ethylene oxidation zone togetherwith a feed containing oxygen and performing a process for preparingethylene oxide to obtain ethylene oxide and carbon dioxide; andproviding at least part of the obtained carbon dioxide to the oxygenatesynthesis zone.
 5. A process according to claim 1, wherein the olefinsobtained in step (d) and/or (f) include ethylene, the process furthercomprising: converting at least part of the ethylene with benzene toobtain styrene monomer and hydrogen; and providing at least part of theobtained hydrogen to the oxygenate synthesis zone.
 6. A processaccording to claim 1, wherein feed comprising at least methane, ethaneand carbon dioxide is obtained from natural gas or associated gas.
 7. Aprocess according to claim 1, wherein feed comprising at least methane,ethane and carbon dioxide comprises in the range of from 0.1 to 70 mol %of carbon dioxide, based on the total content of the feedstock.
 8. Anintegrated system for producing olefins, which system comprises: a. aseparation system, having at least an inlet for a feed comprisingmethane, ethane and carbon dioxide, and an outlet for amethane-comprising feed, an outlet for an ethane-comprising feed and anoutlet for a carbon dioxide-comprising feed; b. a partial oxidationsystem arranged to partially oxidise the methane-comprising feed to asynthesis gas, having an inlet for a methane-comprising feed to receivethe methane-comprising feed from the separation system, an inlet foroxygen, and an outlet for synthesis gas; c. a steam cracking systemhaving one or more inlets for an ethane-comprising feed to receive themethane-comprising feed from the separation system and an inlet forsteam, and an outlet for a cracker effluent comprising olefins; d. anoxygenate-to-olefins conversion system, having one or more inlets forreceiving an oxygenate feedstock, and comprising a reaction zone forcontacting the oxygenate feedstock with an oxygenate conversion catalystunder oxygenate conversion conditions, and an outlet for anoxygenate-to-olefins effluent comprising olefins, including at leastethylene; e. a work-up system arranged to receive at least part of thecracker effluent and at least part of the oxygenate-to-olefins effluentto obtain a combined effluent, the work-up section comprising aseparation system, an outlet for ethylene and an outlet for hydrogen;and f. an oxygenate synthesis system having one or more inlets forsynthesis gas to receive the synthesis gas from the partial oxidationsystem, an inlet for hydrogen and an inlet for a carbondioxide-comprising feed to receive the carbon dioxide-comprising feedfrom the separation system, and an outlet for an oxygenate feedstock;and means for providing the oxygenate feedstock from the outlet foroxygenate feedstock of the oxygenate synthesis system to the oxygenatefeedstock inlet of the oxygenate-to-olefins conversion system and meansfor providing hydrogen from the outlet for hydrogen of the work-upsection to the inlet for hydrogen of the oxygenate synthesis system.